Complexes of Fungal Endoliths in Shells of Cultured Giant Oysters Crassostrea gigas (Ostreidae), Healthy and Infected by the Boring Sponge Cliona vastifica (Clionaidae)

The mycobiota of shells of the oysters Crassostrea gigas, healthy and infected by the boring sponge Cliona vastifica, was studied at the mussel and oyster farm of the Mariculture Research Association LLC (city of Sevastopol, Crimea, Black Sea) in April 2020. 64 species of microscopic fungi from 24 genera, 13 families, 10 orders, 6 classes from the divisions Ascomycota, Basidiomycota, and Mucoromycota were isolated and identified from the endogenous layers of oyster shells. 42 species of fungi were found in the shells of healthy oysters, while 54 species of fungi were found in sponge-infected oysters. The largest number of species belonged to the genera Aspergillus, 13 species (8 species in healthy and 11 species in infected ones) and Alternaria, 14 (8 and 14, respectively), representatives of which can cause opportunistic infections (pathogenicity group BSL-1). 39.5% of opportunistic fungal species and one from the BSL-2 pathogenicity group (Aspergillus fumigatus, frequency of occurrence 6.3%) were found in the shells of healthy oysters. The infected shells contained 45.5% of opportunistic species and five from the BSL-2 group (A. fumigatus, 10.4%, A. flavus, 8.3%, Botryomyces sp., Fusarium oxysporum and Phaeoacremonium parasiticum, 4.2% each). In general, the similarity of the species composition of fungi on healthy and infected shells was 62.5%; 30 common species were detected. It was found in the course of studies that the perforation of oyster shells caused by the sponge Cliona vastifica increases the diversity of fungal species in the endogenous layers of mollusk shells.